<!DOCTYPE html>
<body>
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
  <script>
    var oldhref = window.location.href;
    window.location = "data:text/html,<body>";
    while (window.location.href == oldhref) {
      var xhr = new XMLHttpRequest();
      xhr.open("GET", oldhref, false);
      xhr.send();
    }
    x = 4;
    window.xx = 6;
    watch('x', alert);
    window.watch('xx', alert);
    x = 5;
    window.xx = 7;
  </script>
</body>
